This invention relates generally to aircraft navigation devices, and more particularly to area navigation devices, known in the art as "RNAV" devices. Specifically, the present invention automatically generates waypoints on the four cardinal radials of VORTAC stations wherever those radials happen to intersect the intended flight path. In a presently preferred embodiment, the automatic cardinal waypoint arrangement is incorporated into an RNAV device so as to form an integral part thereof. This application is related to our copending, commonly assigned design patent application Ser. No. 217,382 filed concurrently herewith on Dec. 17, 1980 for Faceplate Including Controls and Digital Readout of Aeronautical Radio Navigation Device.
To help understand the prior art background of the invention, reference should initially be made to FIGS. 1-3. In FIG. 1, there is shown in block diagram, a typical arrangement for a known RNAV device 20. RNAV device 20 is intended for use in combination with at least one conventional navigational system 26 including a VOR output providing the radial course (angular bearing) of an aircraft position with respect to a VORTAC station to which the navigation system is tuned; and a DME (distance measuring equipment) output indicating the distance (range) of the aircraft position from/to that VORTAC station. In addition, RNAV device 20 is used in conjunction with an HSI/CDI (horizontal situation indicator/course deviation indicator) having a steering needle, an omnidirectional bearing selector (OBS) and a "To/From" flag. Such devices are well known and therefore, they will not be discussed in further detail.
A conventional RNAV device, such as RNAV device 20, allows a pilot to establish a waypoint at any arbitrary position that can be defined with respect to a VORTAC station (as long as the pilot can define the radial/distance position of the waypoint with respect to the VORTAC station). Once the pilot has entered data representing the waypoint into RNAV 20, it keeps track of the aircraft's current position with respect to the VORTAC station and reckons the appropriate course to the waypoint established by the pilot. Using an HSI/CDI with a steering needle and an OBS input or other means for navigating along a desired bearing to or from the waypoint, the pilot can fly the RNAV course reckoned by RNAV 20. Thus, RNAV devices have made it possible to define a direct flight path from one way point to another by allowing a pilot to establish intermediate "imaginary" waypoints, not necessarily coincident with VORTAC stations, eliminating the prior necessity of establishing a flight path directly from VORTAC station to VORTAC station. Concurrently, the RNAV device continuously reckons the distance from the aircraft to its designated waypoint.
Referring now to FIG. 2, there is shown a graphical plot illustrating the typical use of a conventional RNAV. Using an RNAV, a pilot can navigate directly from a point of departure A to a destination B by establishing "imagninary" waypoints such as WP#1, WP#2 and WP#3. These "imaginary" waypoints are generally not located at VORTAC stations. Rather, each waypoint is defined with respect to a VORTAC station. Generally, the first VORTAC to be used is near the departure airport. In this example, the first VORTAC used is VORTAC XXX. The pilot selects the location of WP#1 along his route and defines the position or "address" of that waypoint as a radial bearing and distance from VORTAC XXX. Typically, the pilot determines the position of the waypoint with the aid of a map and plotting devices. In the example shown in FIG. 2, the position of WP#1 is 120.degree. radial bearing (from magnetic north) and 37 nautical miles (NM) distance from VORTAC XXX.
Using other convenient VORTAC stations along the route such as VORTAC YYY and VORTAC ZZZ, WP#2 and WP#3 are defined. WP#2 is defined as 9.degree. bearing and 41 NM range from VORTAC YYY. WP#3 is defined as the 350.degree. radial and 45 NM distance from VORTAC ZZZ.
Typically, before the pilot departs, he enters several waypoint addresses into the memory of RNAV 20 and his desired course bearing from A to B into the OBS. After lift off, navigational system 26, supplying radial bearing and distance information to RNAV 20, is tuned to the frequency of VORTAC XXX. RNAV 20 keeps track of the aircraft's position with respect to VORTAC XXX and notes its progress toward the pilot defined WP#1. The pilot can use his RNAV driven HSI/CDI to fly the desired RNAV course (input via the OBS and calculated by RNAV 20) to reach WP#1. At some point along his RNAV course, after passing WP#1, the pilot tunes his navigational system so as to receive the signal from VORTAC YYY and continues flying the desired RNAV course as directed by the HSI/CDI to reach WP#2, and so on.
Referring now to FIG. 3 there is graphically depicted the classic RNAV triangle. This triangle indicates the manner in which known RNAV devices, such as RNAV 20 drive the HSI/CDI so as to permit the pilot to establish a course to a desired waypoint.
The pilot defines a desired waypoint along his flight path. The waypoint is defined by its radial bearing and distance from a selected VORTAC station. Thus the waypoint is defined by a waypoint position vector (known in the art as the "B" vector). The waypoint position vector is entered into the RNAV device as the waypoint address. The aircraft's present position is automatically defined by a radial (bearing) and distance to the aircraft from the selected VORTAC station. Thus, there is defined an aircraft present position vector (known in the art as the "A" vector). The aircraft present position vector is provided as a second input to RNAV device 20 by navigational system 26. RNAV 20 uses the waypoint position vector ("B" vector) and aircraft present position vector ("A" vector) to compute the bearing and range (distance) to the waypoint from the aircraft's present position. This bearing and range, so computed, constitutes the RNAV course line (known in the art as the "C" vector) and it can then be compared to the desired course line entered via the OBS to compute and provide appropriate drive signals to the HSI/CDI. The waypoint address, aircraft present position and the computed bearing and range from the aircraft to the waypoint form the classic RNAV triangle shown in FIG. 3. Of course, there are many different RNAV devices in current use and they may calculate the RNAV course line according to a variety of different methods. However, they are all based upon the classic RNAV triangle shown in FIG. 3.
Typically, RNAV 20 also compares the desired OBS course setting, entered by the pilot from the aircraft's HSI/CDI, with the computed bearing (RNAV course line-"C" vector) and displays the difference as a linear course line deviation on a left/right steering needle.
The use of conventional RNAV thus enhances a pilot's ability to fly more directly from point to point rather than from VORTAC station to VORTAC station. However, the use of conventional RNAV requires the pilot to establish the imaginary waypoints independent of the RNAV device. The pilot must, with the aid of his maps and plotting instruments, determine the position of a desired waypoint and then enter data defining that position into RNAV device 20. Only then can RNAV device 20 compute an RNAV course to that waypoint. Thus substantial pilot attention is required which may divert his attention from other matters.